3.5 Recent Advances in Hologram System Study

Holographic 3D display is a type of display device to reconstruct the optical wave field such that the reconstructed 3D light beam can be seen as the physical presentation of the original object. The difference between conventional photography and holography is that photography can only record the amplitude information for an object but holography attempts to record both amplitude and phase information. Knowing that current image recording systems can only record the amplitude information, holography needs a way to transform the phase information such that it can be recorded in an amplitude-based recoding system.

Figure 3.10(a) illustrates the principle of hologram recording, which uses a coherent light beam. The light is reflected by a mirror as a reference beam and scattered from the object as the object beam. The interference between the reference beam and the object beam is recorded on the photographic plate as a hologram. When the hologram is illuminated by the original reference beam as shown in Figure 3.10b, the reference beam will be diffracted by the hologram to create a light field which closely approximates to the scattered beam from the object in phase, direction, and intensity. In other words, the light field is reconstructed from the observer's point of view, even the original object does not physically appear in its original place. The holography indeed provides a true 3D image reconstruction.

For digital holography, the photographic plate is replaced by the pixelated liquid crystal spatial light modulator (SLM). Several types of SLM exist by either modulating the amplitude or the phase of the incident beam for each pixel [18]. The required size and resolution for SLM are the major technique parameters to provide a satisfactory viewing experience. However, the information stored in the analog photographic plate is extremely large, which becomes a storage problem during the digitization process and a computation problem during the reproduction process for digital holography. The problems will become worse when we want a holographic video, which requires frame refresh in a small time interval. 3D digital video holography requires more research to resolve the above-mentioned challenges and make it commercially available.